Magnet roll developing device

ABSTRACT

A magnet roll developing device for electrophotography comprises a magnet roll and a collar of non-magnetic material, whose outer diameter is equal to or slightly greater than that of the magnet roll. The collar is mounted on the magnet roll to thereby prevent bulging of a magnetic brush on the magnet roll. A magnetic brush control plate is arranged so that the outer end thereof is at least registered or extends slightly outwardly with respect to the outer end of the collar.

United States Patent Kitajima et al.

MAGNET ROLL DEVELOPING DEVICE Inventors: Tadayuki Kitajima, Yokohama;

Hajime Katayama, Tokyo, both of Japan Canon Kabushiki Kaisha, Tokyo, Japan Filed: July 2, 1974 Appl. No.: 485,111

Related U.S. Application Data Continuation of Ser. No. 282,713, Aug. 22, 1972, abandoned.

Assignee:

Foreign Application Priority Data Sept. 6. 1971 Japan 46-68779 U.S. Cl. 118/637 Int. Cl G03g 13/06 Field of Search 118/637, DIG. 24;

355/3 DD, 15; ll7/l7.5; 346/74 ES References Cited UNITED STATES PATENTS Streich, Sr. 118/637 Flint ll8/637 X Primary EttaminerMorris Kaplan Attorney, Agent, or FirmFitzpatrick, Cella, Harper & Scinto [57] ABSTRACT A magnet roll developing device for electrophotography corrgarises a magnet rolland a collar of nonmagnetic material, whose outer diameter is efida lto or slightly greater than that of the magnet roll. The collar is mounted on the magnet roll to thereby prevent bulging of a magnetic brush on the magnet roll. A magnetic brush control plate is arranged so that the outer end thereof is at least registered or extends slightly outwardly with respect to the outer end of the collar.

2 Claims, 5 Drawing Figures PATENTED FEB] 8l975 FIG.

FIG. 30

FIG. 2@

PRIOR'ART.

FlG.3b

FlG.2b

' PRIOR ART MAGNET ROLL DEVELOPING DEVICE This is a continuation, of application Serial No. 282,713, filed Aug. 22, I972, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a magnet roll developing device for electrophotography, and more particularly to such a developing device in which the effective developing width extends from one end to the other end of a magnet roll and which is capable of uniformly developing an entire surface to be developed.

2. Description of the Prior Art Where a magnet roll is used to carry out development, it is defficult to uniform the hair length of the magnetic brush to a predetermined nap condition because the density of the magnetic line of force produced by the magnet roll is greater at the opposite ends of the roll. In other words, the brush bulges at the opposite ende of the magnet roll so that the touch of the brush with respect to a photosensitive medium is more intense at such opposite ends, thus causing a variation in the density of the formed image on the photosensitive medium at the corresponding ends thereof. In order to accomplish uniform development, the magnet roll must have a reduced length of effective area, which in turn means an increased length of the magnet roll itself. Also, the aforesaid bulging of the brush may result in scattered toner which may intrude adjacent bearing portions for the magnet roll.

SUMMARY OF THE INVENTION The present invention solves the above-noted problems by providing a collar of non-magnetic material on a magnet roll at each end thereof. The collar may have an outer diameter equal to or slightly greater than that of the magnet roll. A control plate is arranged so that the outer end thereof is at least registered or extends outwardly with respect to the outer end of the collar The aforesaid bulging in the magnet brush is caused by the sharp end edge of the magnet roll. Such bulging may be completely eliminated, as shown in an embodiment to be described hereunder, by the non-magnetic collar of the present invention which completely covers each end space of the magnet roll. In addition, the nonmagnetic material forming the collar acts to substantially prevent the developer from passing outwardly from the end portion of the magnet roll. Thus, the magnet roll provides an effective width which is substantially equal to that of the photosensitive medium, so that development free of density variation may be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become fully apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of the magnet roll developing device according to an embodiment of the present invention;

FIGS. 2a and 2b illustrate the relationship between the magnet roll and the magnetic brush control plate according to the prior art; and

FIGS. 3a and 3b illustrate the relationship between the magnet roll and the magnetic brush control plate according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT v Referring to FIG. 1 which is a cross-sectional view of the magnet roll developing device according to the present invention, a photosensitive medium or roll 1 may be rotated for predetermined processes to thereby produce an electrostatic latent image on the surface thereof, and then reaches the developing station. These processes may be accomplished in any suitable manner, for example, a three-layer photosensitive medium may be used and subjected to primary charge, simultaneous exposure and discharge, and if required, overall exposure.

The developing station may comprise a casing 2, magnet rolls 5 rotatably journalled to the unshown opposite side plates of the casing (only one such roll 5 is shown, but actually a plurality of them may be used), a developer stirring screw 3 and a control plate 6. The control plate 6 includes a cutting portion 6a for uniforming the hair of a toner magnet brush T formed around the magnet roll 5 to a predetermined nap length, a hair raiser 7 of magnetic material for softening the end of the brush hair and a control portion for controlling the final length of the brush hair.

The control means 6 may thus control the hair length of the magnet brush, but a problem will be encountered in treating the magnet brush at the ends of the magnet roll 54.

According to the prior art, as shown in FIG. 2, a tongue 6b has been provided at each end of the cutting portion 6a beyond the effective area thereof to cut the hair to the magnet brush. In this arrangement, however, some clearance is required between the magnet roll 5 and the tongue 6b and the brush T is restrained in no way after it has passedthe blade, with a result that bulging occurs as indicated at T in FIG. 2b. Such bulging will progressively expand to the inner effective developing area of the roll 5 so that the hair length of the magnet brush in the effective area thereof will beincreased only at the opposite 'end portions of the roll, thus causing a greater touch of the brush-with respect to the photosensitive drum 1 which would in turn cause a variation in the density of the resultant image formed on the drum 1 at the corresponding ends thereof.

The present invention provides a collar 8 of nonmagnetic material mounted at each end of the magnet roll, as shown in FIG. 3a. The collar may have an outer diameter substantially equal to or slightly greater than that of the magnet roll 5. Further, the control plate 6 is arranged so that the outer end thereof is at least registered or extends outwardly with respect to the outer end of the collar 8.

The described bulging T in the magnet brush T is caused by the sharp end edge of the magnet roll 5. Such bulging may be completely eliminated, as seen in FIG. 3b, by the non-magnetic collar 8 of the present invention which completely covers each end space of the magnet roll 5. In addition, the non-magnetic material forming the collar 8 acts to substantially prevent the developer from passing outwardly from the end portion of the magnet roll. Thus, the magnet roll 5 provides an effective width which is substantially equal to that of the photosensitive drum 1, so that no variation occurs in the density of the formed image on the drum 1 at the opposite ends thereof. In this case, the end of the control plate 6 may be at least registered or extend slightly outwardly with respect to the edge 8 of the collar 8. The problem of scattered toner and is intrusion into the bearing portions for the magnet roll may also be solved by the described arrangement of the present invention. Furthermore, if the entire surface of the photosensitive drum is to be uniformly developed, good development may be achieved without the need to make the magnet roll longer than necessary.

We claim:

1. A magnet roll developing device for supporting a magnet brush for electrophotography comprising a magnet roll having a plurality of magnets arranged axially along the circumference thereof parallel to the axis of said roll in such a way that respective adjacent magnets are of opposite polarity, a pair of collar means of non-magnetic material, each having an outer diameter equal to or slightly greater than that of said magnet roll,

and magnetic brush control means disposed axially adjacent said roll, said pair of collar means being mounted respectively at opposed ends of said magnet roll to prevent bulging of said magnetic brush at said ends of said magnetic roll, said magnetic brush control means comprising a plate member having a cutting portion for cutting said magnetic brush to a predetermined uniform nap length, a nap raising portion for softening the periphery of said brush, and a cutting portion for controlling the final radial length of the brush and said magnetic brush control means being arranged so that its opposed ends extend at least into radial alignment with the outer ends of said pair of collar means.

2. A magnet roll developing device according to claim 1, wherein said nap raising portion comprises a magnetic plate. 

1. A magnet roll developing device for supporting a magnet brush for electrophotography comprising a magnet roll having a plurality of magnets arranged axially along the circumference thereof parallel to the axis of said roll in such a way that respective adjacent magnets are of opposite polarity, a pair of collar means of non-magnetic material, each having an outer diameter equal to or slightly greater than that of said magnet roll, and magnetic brush control means disposed axially adjacent said roll, said pair of collar means being mounted respectively at opposed ends of said magnet roll to prevent bulging of said magnetic brush at said ends of said magnetic roll, said magnetic brush control means comprising a plate member having a cutting portion for cutting said magnetic brush to a predetermined uniform nap length, a nap raising portion for softening the periphery of said brush, and a cutting portion for controlling the final radial length of the brush and said magnetic brush control means being arranged so that its opposed ends extend at least into radial alignment with the outer ends of said pair of collar means.
 2. A magnet roll developing device according to claim 1, wherein said nap raising portion comprises a magnetic plate. 